Hymenagaricus ruber Ralaiv., Liimat. & Niskanen, in Cao et al., Fungal Diversity 132: 513 (2025)

Index Fungorum number: IF 903129; MycoBank number: MB 903129; Facesoffungi number: FoF 17104; Figs. 1, 2

Etymology – ruber (Latin) = red, refers to the colors of the basidiomata.

Holotype – K-M 251793.

Pileus 1 cm in diam., at first convex, then low convex and slightly depressed in the center; deep red in the center, followed by a white zone, especially when older, then pale pink towards the margin; surface dry, with appressed plate like scale(s) in the center, with minute squamules towards the margin. Lamellae free, close, edge even, with lamellulae, white. Stipe up to 3 cm long, up to 4 mm wide, central, white at the very top of the stipe, pink lower down, surface at the top of the stipe with small squamules, woolly-squamulose lower down, cylindrical. Context not recorded. Odor and Taste not recorded.

Basidiospores 5–6.5 × 3.5–4.5(–5) µm, ellipsoid, smooth, brown in KOH, yellow brown in Melzer’s reagent. Basidia (in KOH) 12–14 × 6–6.5 µm, sterigmata 1–3 µm long, subcylindrical to pyriform, usually 2-, 4-spored, rarely 1-spored, not clamped, hyaline. Cheilocystidia variable in size and form, 8.5–17 × 5–7.5 µm, subutriform (Fig. 1d); 16–26 × 3.5–5 low clavate to elongate (Fig. 1e). Pileipellis cutis made of parallel, non-septate hyphae up to 3.5 µm wide, with a pale olive color in Melzer’s reagent.

Habitat – Dry, deciduous, tropical forest, on white sandy soil.

Distribution – So far only known from Madagascar.

Material examined – MADAGASCAR, Mahajanga, Boeny Region, Ankarafantsika National Park, north side of Lake Ravelobe, dominated by Euphorbiaceae, Rubiaceae, Malvaceae, Celastraceae, Ebenaceae, 19 Feb. 2018, coll. S. Morris, MAF18-141 (K-M 251793, holotype; TAN, isotype).

GenBank – K-M 251793: PQ636523 (ITS).

Notes – Hymenagaricus ruber has basidiomata with whitish red, pink and pale pink colors, two types of cheilocystidia and ellipsoid, small spores 5–6.5 × 3.5–4.5(–5) µm. ITS sequence (GenBank PQ636523, holotype) is distinct from the other members of the genus Hymenagaricus and deviating from them by more than 5% (> 40 substitutions and indels). In our phylogenetic analysis, the new species forms a group with other species of Hymenagaricus, but with a very low support (BS 56%) and Heinemannomyces splendidissimus (a monotypic genus described from Asia in 1998). At the moment, we place the Malagasy species in this group and use the genus name Hymenagaricus that being the older name, has priority over Heinemannomyces.

Figure 1 – Hymenagaricus ruber (K-M251793, holotype). a Basidiomata. b Basidiospores. c Basidia. d, e Cheilocystidia. f Pileipellis. Scale bars: a = 1 cm, b–f = 10 µm. Credit: S. Morris (a), Anna Ralaiveloarisoa (b–f).

Figure 2 – The best scoring RAxML tree with a final likelihood value of -4096.148654 of the genus Hymenagaricus and Agaricus based on the ITS region. Related sequences were retrieved from GenBank. Thirty-eight specimens were included in the analysis of the ITS region which comprises 782 characters after alignment. The tree is rooted with Coniolepiota spongodes (KC625531) and Coniolepiota spongodes (MW080627). The matrix had 334 distinct alignment patterns, with 10,61% of undetermined characters or gaps. Estimate base frequencies were: A = 0.227093, C = 0.213184, G = 0.241131, T = 0.318593; substitution rates AC = 1.046018, AG = 3.987882, AT = 1.146073, CG = 0.203864, CT = 5.408419, GT = 1.000000. Maximum Likelihood bootstrap values greater than 50% are given near to each branch. The type specimens are in bold. The new species are in blue. Names, other than those originating from the type specimens, are only indicative and not confirmed via comparison with sequences from type specimens.